This application claims the benefit of a Japanese Patent Application No. 2000-354898 filed Nov. 21, 2000, in the Japanese Patent Office, the disclosure of which is hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to optical fixing toners for use in visualizing an electrostatic latent image which is formed on a surface of a photoconductive insulator such as a photoconductive drum, and more particularly to an optical fixing toner which forms a toner image transferred onto a recording medium such as paper from a photoconductive insulator and is melted and fixed on the recording medium when irradiated with light.
2. Description of the Related Art
The electrophotography technique is one method of visualizing electronic image data on a recording medium. According to the electrophotography technique, an electrostatic latent image is formed on a surface of a photoconductive insulator, and a toner is adhered on the latent image to visualize the latent image into a toner image. Then, the toner image is transferred onto a recording medium such as paper, and a print is obtained by melting and solidifying the toner of the toner image on the recording medium.
The toner image is formed on the surface of the photoconductive insulator by applying a uniform electrostatic charge on the surface of the photoconductive insulator by corona discharge, for example, forming an electrostatic latent image by irradiating an optical image on the photoconductive insulator by an appropriate means, and adhering a charged toner on the electrostatic latent image by an electrical attracting force thereof. The toner which is used to develop the electrostatic latent image includes a binder resin which is made of a natural or synthetic polymer material admixed with a coloring agent, and an additive such as a charge control agent if necessary, and the toner grains have a diameter on the order to 1 to 3 xcexcm.
As methods of fixing the toner image which is transferred onto the recording medium, there is a method which presses or heats or combines pressing and heating so as to melt and then solidify the toner, and an optical fixing method which irradiates light so as to melt and then solidify the toner.
Recently, much attention is drawn to the optical fixing method which uses light, because this method is unaffected by undesirable influences of the pressing and/or heating. In other words, the optical fixing method does not require the toner image to be pressed when fixing the toner, and for this reason, there is no need to make a fixing roller contact or press the toner image, and a deterioration of an image resolution or reproducibility during a fixing process is suppressed. In addition, there is no need to provide a heat source such as a heater within the fixing roller in order to heat the toner image. Therefore, according to the optical fixing method, it is unnecessary to wait until the heat source reaches a desired temperature after the power is turned ON, and the printing can be carried out immediately after the power is turned ON. Moreover, heat source, a temperature rise within an apparatus can appropriately be avoided. Furthermore, even when the recording medium is jammed within a fixing unit when the apparatus fails, for example, safety is ensured since there is no possibility of the jammed recording medium burning and generating fire due to the heat from the heat source.
When employing the optical fixing method, it has be conventionally proposed to add a light absorbing agent in the toner so that the toner can efficiently absorb and utilize the energy of the light irradiated thereon. For example, a Japanese Laid-Open Patent Application No.61-132959 proposes a method of melting the toner by irradiating light in an infrared region by use of a xenon flash lamp, wherein an aminium-salt-based compound or a diimomium-salt-based compound is added as an infrared ray absorbing agent. The aminium-salt-based compound or the like has a good infrared ray absorbing characteristic, and has a relatively light color tone in the visible region. Accordingly, it is possible to suppress undesirable effects on the color tone of the fixed image, and the aminium-salt-based compound or the like is suited for use as the infrared ray absorbing agent for a color toner.
However, as described above, the charge control agent may be added to the toner. The charge control agent is added to control the charge of the toner within a desired range, so as to enable an appropriate printing. The charge control agent is made of a polar compound such as tertiary amine having portions with high polarity or, a highly reactive ionic compound such as quaternary ammonium salt. But when a highly reactive compound such as the charge control agent exists within the toner, the counter ion within the aminium-salt-based compound or the like are subject to abstraction by the polar group or, an ion-exchange occurs between the counter ion and the ionic compound, thereby changing the structure of the aminium-salt-based compound or the like. In addition, due to the heating caused by the mulling carried out during the toner fabricating process, the aminium-based-salt compound or the like which are organic materials may undergo a structural change or react with the polar group. When such a structural change occurs, the light absorbing band (wavelength) shifts, and the infrared ray absorbing characteristic of the aminium-based-salt compound or the like deteriorates, such that the infrared absorbing characteristic is completely lost in a worst case.
On the other hand, the charge control agent also undergoes a structural change due to a reaction with the aminium-based-salt compound or the like, and the charge control characteristic is deteriorated thereby. Moreover, although the aminium-based-salt compound or the like originally has the light color tone, the color tone is changed to a yellowish brown, for example, when the structural change of the charge control agent occurs. Such a change in the color tone affects the color tone of the color toner image after the fixing process. In the case of a red color toner, for example, the toner image on the recording medium after the fixing process becomes reddish brown when the structural change of the charge control agent occurs.
Therefore, the organic materials such as the aminium-based salt compound are relatively good infrared ray absorbing agents, but still require improvement to overcome the problems described above.
Accordingly, it is a general object of the present invention to provide a novel and useful optical fixing toner in which the problems described above are eliminated.
Another and more specific object of the present invention is to provide an optical fixing toner which eliminates the problems of the conventional infrared ray absorbing agent, by including an infrared ray absorbing agent which can realize a satisfactory infrared ray absorbing characteristic even when a polar compound such as tertiary amine having portions with high polarity or a highly reactive ionic compound such as quaternary ammonium salt coexists.
Still another object of the present invention is to provide an optical fixing toner comprising an infrared ray absorbing agent made of one element or a mixture of a plurality of elements selected from a group of elements consisting of oxides, sulfides, halides, complex salts and acid chlorides of lanthanoide. According to the optical fixing toner of the present invention, a lanthanoide-based compound is an essential constituent element of the infrared ray absorbing agent. Since the lanthanoide-based compound has absorption in the infrared region having a wavelength of 700 nm or greater, the lanthanoide-based compound gives the optical fixing toner an infrared ray absorbing characteristic. When an infrared ray is irradiated on the optical fixing toner of the present invention, the infrared ray having the wavelength of 700 nm or greater is efficiently absorbed by the lanthanoide-based compound, and an energy of the irradiated ray is transformed into a thermal energy which melts a binder resin of the optical fixing toner. Therefore, the optical fixing toner of the present invention has a good optical fixing characteristic.
In the optical fixing toner, a content of the infrared ray absorbing agent within the optical fixing toner may be in a range of approximately 0.1 to 20.0 weight percent.
In addition, at least a portion of the infrared ray absorbing agent may be externally added to surfaces of toner grains forming the optical fixing toner.
Moreover, the lanthanoide may be made of an element selected from a group of elements consisting of salts, complex salts and oxides of ytterbium, neodymium and samarium.
Further, the optical fixing toner may further comprises an aminium-salt-based compound described by a formula (1), and/or a diimomium-salt-based compound described by a formula (2), 
where R1 through R4 denote hydrogen atom, alkyl group, substitution alkyl group, cyclic alkyl group, alkenyl group, alalkyl group or substitution alalkyl group, A denotes a p-phenylnene group or p-biphenylene group, and X denotes negative ion.